AIM:To evaluate the sensitivity and specificity ofabdominal ultrasound (US) for the diagnosis of hepaticsteatosis in severe obese subjects and its relation tohistological grade of steatosis.METHODS:A consecutive series of obese patients,who underwent bariatric surgery from October 2004to May 2005,was selected.Ultrasonography wasperformed in all patients as part of routine preoperativetime and an intraoperative wedge biopsy was obtainedat the beginning of the bariatric surgery.The US andhistological findings of steatosis were compared,considering histology as the gold standard.RESULTS:The study included 105 patients.The meanage was 37.2 + 10.6 years and 75.2% were female.The histological prevalence of steatosis was 89.5%.The sensitivity and specificity of US in the diagnosis ofhepatic steatosis were,respectively,64.9% (95% CI:54.9-74.3) and 90.9% (95% CI:57.1-99.5).The positivepredictive value and negative predictive value were,respectively,98.4% (95% CI:90.2-99.9) and 23.3%(95% CI:12.3-39.0).The presence of steatosis onUS was associated to advanced grades of steatosis onhistology (P = 0.016).CONCLUSION:Preoperative abdominal US in our serieshas not shown to be an accurate method for the diagnosisof hepatic steatosis in severe obese patients.Until anothernon-invasive method demonstrates better sensitivityand specificity values,histological evaluation may berecommended to these patients undergoing bariatricsurgery.